No not police to police , its population to population.
Simples . draw the graph . Roughly 8,7, 4 up the side. Mark along 4 time periods.
The line cuts downwards about 19th October 2017 give or take a few police.

Hello there NICKNAMENICK...

My friend I spent a lot of years in the coppers and your mathematical equation(s) have me utterly confounded! As does many of your other contributions have done so as well. It's no wonder I only made it to sergeant? May I ask if you are/were an Actuary? A Scientist perhaps or any other profession that has an entry level of genius? To become a police-person, you must demonstrate your have an IQ of two points above that of plant life, so as you can see, they set the bar relatively high.

I'm glad we have many other more erudite contributors herein, who can fathom precisely what it is you're attempting to impart. I'm dreadfully sorry Mr NICK, but I must therefore confess, I'm nothing more than a simple dullard; still I'm trying hard to keep up with the Topic nevertheless. Invariably though, all those myriad of numbers, that are merely swirling and spiralling about my head intermittently, without making any logical sense, or by assisting me to fully comprehend their true nature or import; for this reason alone I must respectfully withdraw from the discussion forthwith.

Statistics can be baffling can't they?

Look at it like this...you've got to bring the numbers back to a common denominator in order to make comparisons.

One cop per 765 people equals 1.31 cops per 1000.
One cop per 693 people equals 1.44 cops per 1000.
one cop per 417 people = 2.40 cops per 1000.

So they've had an increase of 0.13 cops per 1000 people in first period and 0.96 cops per 1000 people in second period.

So clearly the rate of increase is increasing - by around 7 times. Even if that were to be maintained (it isn't, but just for pretend) it doesn't get us within cooee of your date.

Sometimes they aren't lies or damned lies...they're just misunderstood statistics.

Hi there MHAZE...This thoroughly stupid retired ol' copper humbly thanks your, for clearly enlightening me on how our friend Mr NICK'S; hitherto complicated equation is solved. At school the word Arithmetic, would strike terror into the hearts and minds of many of my fellow class mates. And even now, approaching nearly 70 years onward, the word still does have that effect upon me, at nearly 80!

In effect , each one lost about half his customers with the bulk going at the end of the 1900s. The remaining half will rapidly scatter .

" one cop per 417 people = 2.40 cops per 1000.
So clearly the rate of increase is increasing - by around 7 times."

Doing Police recruitment that way gives 16.28 Police Officers per 1000 in year 2051 . However the irresistible force of common-sense gives 7x7 rate of increase , 49x2.4 =118 per 1000 in 2051 . After that it's 49x7 increase, 343 x 118 Police Constables per 1000 and Britain will have no problems and no lunacy .

You know ladies and gentlemen, I've been called many things in my career, some of them most unsavoury, a few even complimentary, but this is the first time, I've ever been reduced to a mere fraction? It's a funny feeling be described as, Constable O.40 or something similar?